The energy recovery wheel may be de-energized for the purpose of providing economizer (free cooling)
operation. This can be achieved with a signal from a Temperature or Enthalpy sensor mounted in the supply air
inlet compartment (see FIGURE 13). This Primary sensor will de-energize the energy wheel when the outdoor air
temperature (factory default is 65°F) or enthalpy (factory default is the ‘D’ setting) is below the field adjustable
set point. An additional Override temperature sensor is also furnished in the supply air inlet compartment to
deactivate economizer mode (see FIGURE 13). The Override (with field adjustable set point) is set at some
temperature lower than the Primary sensor (factory default is 50°F). Effectively, the two sensors create a
deadband where the energy recovery wheel will not operate and free cooling from outside can be brought into
the building unconditioned.
Testing
(terminals referenced below are in the unit control center — see FIGURE 5, Item #7)
Temperature sensor with Override
• Turn both Temperature and Override
thermostats down as low as they go.
The wheel should be rotating.
• Turn the Temperature sensor up as
high as it goes, and keep the Override
sensor as low as it will go. The wheel
should stop rotating.
• Turn both sensors as high as they will
go. The wheel should start rotating.
• Set the Temperature sensor to the
desired temperature for economizer
operation to begin. Set the Override
sensor to the desired temperature for
economizer operation to end (factory
default is 65°F and 50°F, respectively).
Enthalpy sensor with Override
• A factory-installed 620 ohm resistor is
connected across terminals SR and +.
The Override sensor should be turned
down below current temperature in unit. Turn the unit on; LED on the sensor should be off. Check
continuity across terminals 2 and 3, there should not be continuity. There should be continuity
between terminals 1 and 2.
• Disconnect the 620 ohm resistor from terminals SR and +. LED should turn on. There should be
continuity between terminals 2 and 3. There should not be continuity between terminals 1 and 2.
• Turn the Override sensor above current temperature in unit. There should be continuity between
terminals 3 and 6. Set the Override sensor to the desired temperature for economizer operation to end
(factory default is 50°F).
• Reconnect the factory-installed jumper.
10
ECONOMIZER APPLICATION/OPERATION
Enthalpy Sensor
(Primary Sensor)
Timed Exhaust
Frost Control
Override
Probes
FIGURE 13
